W126 sudden heat loss - Page 3 - PeachParts Mercedes-Benz Forum

MS Fowler · #31 03-06-2013, 08:37 PM

Just to say the obvious, ( somebody has to) Is the coolant level full?

LandYaghtLover · #32 03-06-2013, 08:54 PM

Yup. Burped, purged, etc. And its newer coolant. And even more new added when I replaced the t-stat in an attempt to resolve this. G-05 stuff.

Gilly · #33 03-06-2013, 09:14 PM

Remember the emergency default (ie NO power to the valve) is full heat.

LandYaghtLover · #34 03-06-2013, 09:16 PM

Right. So since it went default and I got tons of heat, be at low speed, I should have full heat with it unplugged. if I do, its one more part of the puzzle.

edit: before, I did not get any heat unplugged.

Ritchie · #35 03-07-2013, 08:22 AM

Quote:

Originally Posted by LandYaghtLover

Found it. Its under some electronics and a hood switch.

I am curious. What does that switch do? I have been searching to find out but to no avail.

I know you replaced the monovalve but it still has the symptoms of a bad monovalve. My car did the same thing; some heat at low speeds and no heat at highway speed. The diaphram was damaged. I installed a MTC monovalve and it worked correctlly. It has been about 6 months now and it is still working fine. Maybe try another cheapie MTC monovoale, seems they might be a little hit&miss as far as working right.

LandYaghtLover · #36 03-07-2013, 05:45 PM

Pretty sure the switch is part of the alarm system.

I have full egg-cooking heat though at low speeds. And when the system went into default on the highway I had full heat at low speed (when default, low speed fan is only option).

I am going to pull the plug on it tonight now that I am home early. I will see how the heat works over the next couple of days.

LandYaghtLover · #37 03-08-2013, 05:36 PM

Disconnected the new mono valve and have tons of uncontrollable heat. Figures. That rules out air pockets, etc.

hapsdoggen · #38 10-24-2013, 08:15 AM

Quote:

Originally Posted by LandYaghtLover

Disconnected the new mono valve and have tons of uncontrollable heat. Figures. That rules out air pockets, etc.

did you find the problem...?

i am having the same problems....

did you repair your monovalve with the MTC repair kit or did you buy and OEM monovalve...?

LandYaghtLover · #39 10-25-2013, 09:43 PM

I did not find the issue for certain yet. I did replace the parts with MTC. No change. So I took it apart again. This time I baked the solenoid on the over.

What I found is that the valve was leaking a bit. I think this flooded the solenoid. From what I can see, the solenoid was causing some electrolysis of the coolant by being exposed to it!!!

Anyway, after expensive cleaning and "drying out" I now have 100% heat at all times. Given that winter is here, I am okay with that for now. But when I have time I plan to remove the solenoid again and see how it moves when I adjust the temp. The plunger should move in and out. Voltage at the connector is fine and working with controls.

If I had a spare solenoid, I would just swap it out to test.

C Holmes · #40 11-03-2013, 07:13 AM

Does anyone here know if a monovalve from a w124 will work on the w126? They physically appear different but maybe an updated version as 124 is a 94 and 126 is a 90. I have a spare from the 124 and I think my 126 needs one.

sam196370 · #41 11-14-2013, 02:02 PM

I have a 91 560SEL and when I got it 6 years ago the monovalve was bad, replaced it and haven't had a problem until recently. Same issue, around town heat works GREAT, once on hwy it turns off. Just bought a genuine MB monovalve today from Pelican Parts, I've learned the hard way that when it comes to important stuff like heat or engine gaskets I always go genuine; cosmetic stuff I buy aftermarket - and am still disappointed by the low quality.

Sounds like your issue is still the MV.

C Holmes · #42 11-14-2013, 02:34 PM

Ya I am sure it is the M valve. I bought the "kit" from aftermarket and it will not fit in the electromagnet (waaay too tight) so I removed the circlips and swapped out the other parts. Put it in and had heat! till I got to highway

Anyway now not sure what to do with it. Need heat I live in Nova Scotia. Not sure why it wont work now tho, It really should I think.

LandYaghtLover · #43 11-14-2013, 07:09 PM

Does your engine temp stay constant? Next just disconnect the valve. With it disconnected you should have full heat at all times.

C Holmes · #44 11-14-2013, 07:54 PM

Temp is a constant 80. I will try unplugging the darn thing and see what's up. If I get out and squeeze the heater hoses I can get heat.

C Holmes · #45 11-15-2013, 06:18 AM

well unplugging it didn't work, Not sure where to go from here. I don't think the core is plugged the car doesn't have very many miles on it and has always been serviced with new coolant and such. The old M valve did have a torn bellows so pretty sure that must be it. Is there any way to test it on the bench? I'm not even sure what it is supposed to do. Like I said I had to take the old one apart and put the new ones parts on it as the new one didn't fit very well. Maybe it is just crap to start with. When I had it apart the aux pump was working as I checked it and could see the coolant flowing in the valve. The hoses are not hot so safe to say no coolant getting in the core. If I squeeze them I have heat for a bit. Nothing is ever straight forward it seems.